Plan B aftermath

My husband & I had intercourse last week & he accidentally finished inside of me. Last Monday I purchased a Plan B pill, everything was fine until late last week. I've taken these pills in the past but not any time recently to cause such symptoms. I started getting stomach cramping but instead of close to my pelvis where mebstrual cramps usually are, they carried up top. On top of that I've been having bleeding almost like a period. I had my period this month already & wasn't expected until the 2nd week of October. Any idea of what's going on?